Treatment of cellulosic pulp



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Patented Jan. 30, 1945 j Cross Reference No Drawing.

' '7 Claims.

Thisinvention. relates to treated. cellulosic pulp and the method oftreatment. Moreparticularly the invention. relates t the. making; of a.wood pulpv of reduced and stabilized. viscosity by treatment withhydrogen peroxide in; proportion. that is very small in relation to the'amount of pulp I treated and in conjunction with a metal. of kind to bedescribed.

The use of hydrogen peroxide to lower the viscosity of wood pulp hasbeen known heretofore. It has been necessary, however, to use relativelylarge proportions of the peroxide.

I have now discovered that at least equal reduction in viscosity andbetter control of the oporation may be effected by the use of much.smaller proportions of peroxide than heretofore necessary provided thetreatment with peroxide is. made in the presence of iron, copper,aluminum, manganese, or like metal. v

The invention comprises the. method of treatment of pulp with thelimited proportion of peroxide and the metal and. also theresultingproduct. In the preferred embodiment, the invention comprisessuch treatment of pulp that has been previously reduced to asubstantially pulverulent condition, effecting the treatment at a pHof'approximately 6 to Band using the hydrogen peroxide on the anhydrousbasis in proportion not substantially greater than 1% of the weight ofthe pulp and at a temperature between about 130 and. the boiling pointof'the aqueous solution of the peroxide at the prevailin pressure,preferably between about 180 and212 F. To avoid continuance of'thereaction and objectionable uncontrolled Variations of viscosity as theproduct stands, remaining peroxide is re moved, as by centrifuging andrinsing, after the viscosity is lowered'to the desired level.

Proceeding as described there is obtained the desired reductioninviscosity of the cellulose without'other objectionable change. Thusthe viscosity of alpha cellulose may be lowered to a tenth or less ofthe original, as from about 6,000 to 700 or even 100'or 200 centipoisesas measured by test in sodium 'zincate solution. In this test there isformed a solution of the cellulose in standard concentration in astandard (10%) solution of sodium zincate and. the viscosity isdetermined by the Stormer or an improved form of such viscosimeter.

The cellulose that has been so reduced in vis cosity is suitable for usein making commercial solutions of cellulose in sodium zincate forapplicatlon to textiles or thelike and subsequent precipitation of acellulose coating by the addi- Application September 10, 1942;" SerialNo. 457,889

tionof. sulfuric acid: in amount to neutralize the alkalinityofthezincate solution. The treated pulp may also-be used to makevcellulose xanthate solutions. for the manufacture of: rayon or cellulosesheeting when low viscosity cellulose is desired. Also, the treated pulpis suitablefor nitration. in making pyroxylin for lacquer solutions.

As the cellulose used, there is employed wood pulp, cotton linters,rayonwaste. or other pulp. that is largely or practically entirelycellulose. Wood pulp and cotton are the preferred materials because oftheir relatively low cost and suitability. If wood pulpisused, the kindchosen is preferably a. purified grade: known as alpha cellulose.Thevcotton used is suitably that which.

has been purified by alkali digestion, to. remove undesired ingredients.

In any case, the cellulose tobe used: should. be in a state of finesubdivision and preferably substantially pulverulent so thatit isreacted upon readily andsubstantially uniformly by the peroxide treatingsolution. A. spun. thread, for ex.- ample, is not satisfactory. Neither.is a: fabric. While av usual loose. pulp. may beusedunder somecircumstances, the cellulose. for best results must be finely divided. I

Such a. substantially pulverulent. cellulose is made by grinding orpreferably cutting the se lected cellulose to such. fineness that itwill pass largely through a 30-mesh. screen or preferably through aBO-mesh screen. Actually I prefer to use cellulose which is,predominantly IOU-mesh or finer, difficulty having. been found withmaterial of the coarser meshes from lumping of the cellulose in thetreating solution.

Thefmoisture content during the comminuting of the cellulose may be thatwhich is normally present in the air-dried material. ,When the moisturecontent is much higher, the cellulose may be made into a slurry andground in a ball mill.

The viscosity reducing combination is hydrogen peroxide in contact withiron; copper; aluminum, or manganese; iron being particularly effectiveand constituting the preferred metal particularly when in the form ofstainless steel. Stainless steel as the container for the. reactionmixture is very satisfactory commercially inproviding an adequate supplyofiron and avoidin such an excess as might cause i ron' discoloration ofthe product.

The metal may be in. massive form, as, for, example, in the form of thecontainer in which the reaction mixture is held or as a few added nails,or inthe formof small pieces or line powder pro- Search Room vided thereare no objections to the difficulty experienced in separating smallpieces from the product or to some discoloration from the use of suchpieces. In other words, the metal is present in elemental form.

The metal accelerates the reaction and makes unnecessary a largepro-portion of peroxide.

As the peroxide, only hydrogen peroxide is satisfactory. I I

The concentration of the peroxide solution which contacts the celluloseis very limited. There is thus provided better control of the reactionwhich, in the presence of the metal, is satisfactory in speed even atthe low concentration of the peroxide. If a long time is to be allowedfor the reaction, say a day or so, the concentration of the peroxide inthe treating solution may be as low as 0.001%. Ordinarily there is usedan aqueous solution of 0.001 to 0.1% concentration of hydrogen peroxide,all proportions of peroxide being given herein on the anhydrous basisunless specifically stated otherwise. Stronger solutions are notrequired or justified on the basis of cost. Ordinarily I use a solutionof hydrogen peroxide of concentration about 0.003 to 0.03%.

It will be understood that the rest of the solution is ordinarily waterand the concentrations given are the concentrations of hydrogen peroxidein the water solution which bathes the cellulose at the beginning of thetreatment described.

It is very important to control the total amount of peroxide used inproportion to the cellulose being treated. Thus, it is necessary to useapproximately 0.1 to 1 part of actual hydrogen peroxide for 100 parts ofthe cellulose Ordinarily I start with a commercial 30% solution ofhydrogen peroxide containing the conventional proportion of acid orother stabilizer for the hydrogen peroxide and add this to sufiicientwater at a temperature of around 210 F. to lower the proportion ofperoxide to'one of the concentrations given above. So much of theoriginal 30% hydrogen peroxide is used as required to give about 0.1 to1 part for 100 parts of the cellulose and to wet all the cellulosethoroughly. This amount is usually about 5 to parts for each part of thecellulose. The cellulose is then introduced rapidly and vigorouslystirred into the solution. The

' v solution is heated approximately to the boiling point. The pH isestablished at 6 to 8. The cellulose, being added at ordinarytemperatures, lowers somewhat the temperature, say to 180 F. or so, andthe mixture is stirred at about this temperature for about an hour ortwo. The peroxide is then separated, as by centrifuging, so that theperoxide is removed from the remaining treated cellulose. Preferably thematerial is rinsed with cold water in the centrifuge till substantiallyfree from peroxide, so that further uncontrolled reaction is avoided.

If the pH of the mixtur as first made and before the warming to lowerthe viscosity of the cellulose is not within the range of approximately6 to 8, a usual acid, alkali, or buffer as may be required is added toadjust the pH to that range. For a pH on either side of that range,there is a decreased rate of reaction of the hydrogen peroxide and metalcombination in lowering the visccsity of the cellulose.

Example 1 Nine gallons of water are warmed to 210 F. in a stainlesssteel container provided with an agitator. One pound of commercial 30%hydrogen peroxide is added to the liquid. Then 100 pounds of 92% alphacellulose pulp which has been previously cut to 100-mesh fineness areadded at one time. The mixture is agitated for about one .hour, duringwhich time the mixture slowly cools.

The cellulose slurry is then discharged to a centrifuge and thecellulose is freed of the liquor as far as possible and finally washedwith warm water. The pulp is then dried in an air drier or is used inthe wet state for making solutions.

The initial viscosity of the cellulose before this treatment would beabout 6,000 centipoises by, the standard method described and aftertreatment about 1,000 centipoises.

Example 2 One hundred. pounds of pulp as described in Example 1 areadded to 100 gallons of water at F. containing 3 pounds commercial (30%)hydrogen peroxide. This mixture is agitated for 24. hours in a woodentank into which small pieces of iron have been introduced. After 24hours the cellulose is separated from most of the remaining liquor in afilter press and thoroughly washed with warm water.

The viscosity change due to this treatment will be of the same order asin Example 1.

Example 3 The procedure of Example 1 to 2 is followed except that theprevailing pressure on the mixture is made superatmospheric, say 10 to40 pounds gage, and the batch is heated to approximately the boilingpoint of the peroxide solution in an autoclave.

Example 4 The treated cellulose from any of the above treatments issubstituted pound for pound in making cellulose zincate solutions inaccordance with the description given in U. S. Patent No. 2,322,427,issued June 22, 1943, on an application filed August 19, 1941, forCellulose product.

It will be understood that it is intended to cover all changes andmodifications of the exthe boiling point of the aqueous solution under ithe prevailing pressure until the viscosity is reduced to the desiredlevel, separating remaining hydrogen peroxide from the treated pulp, andthen drying the product, the cellulosic pulp being of such finenessbefore treatment with the peroxide that the pulp will pass largelythrough a 30 mesh screen.

2. In making a cellulosic pulp of lowered viscosity, the method whichcomprises forming a mixture of wood pulp, of such fineness as to pass inpredominating proportion through a 60 mesh screen, with a dilute aqueoussolution of hydrogen peroxide at a pH of about 6 to 8 and warming themixture in contact with a metal in elemental form selected from thegroup consisting of iron,

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copper, aluminum, and manganese to effect the desired lowering ofviscosity.

3. Th method described in claim 2 the proportion of the hydrogenperoxide being not substantially in excess of 1 part on the anhydrousbasis to 100 parts of the cellulosic pulp.

4. The method described in claim 2, the wood pulp before mixing with thehydrogen peroxide solution being previously reduced to substantiallypulverulent condition causing the pulp to be so fine as to pass inpredominating proportion through a 60 mesh screen and the aqueoussolution of the peroxide being used in amount to wet thoroughly all ofthe cut wood pulp before the warming is undertaken;

5. The method described in claim 1, the metal used being iron.

tress tteierance tions recited in claim 1, the said pulp being a powderof fineness to pass in predominating proportion through a 60 mesh screenand of such low viscosity that when dissolved in aqueous sodium zincatesolution in the proportion of 5 parts of the pulp to. 100 parts of thezincate solution, the

viscosity of the resulting solution at. 25 C. is 100 1 to 1500centipoises.

SENEY M. EDELSTEIN.

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